2024-2025 Physiology Lecture Notes (University of Galway)

Physiology School of Medicine Founded in 1845 2024-2025 Course: MD137 Introduction to Physiology Lecturer: Lecture 2:...

Physiology School of Medicine Founded in 1845 2024-2025 Course: MD137 Introduction to Physiology Lecturer: Lecture 2: Leo Quinlan RMP [email protected]  2 Cells of the Nervous system Resting membrane potential Bioelectricity Learning Outcomes 4 What is meant by resting membrane potential (RMP). Describe the main players in formation of RMP. Explain the formation of the nerve RMP. Explain why nerve RMP is near -70mV. Explain how potassium can kill your patient !!! Excitable 5 Central Neurons  h axons from the leg can be le. Additionally, erse recording and stimulation oap without o many anyexercises. laboratory Excitable peripheral Single-stranded, Neurons 6 the top of insect amplifiers (see nel, extracellular 00 Hz) and low- Hz notch filters A). Methods for fier with similar Figure 1. Recording and Excitable peripheral Neurons 7 Bioelectricity 8  Luigi Galvani tested whether Bioelectricity 9 electrical energy from storms was the same electricity found in nerves in the body. When lightening struck the wire, the electricity stimulated the frog nerves causing the legs to move. His experiments showed that the electricity found in nature and the electricity found in neural systems are the same. "Perhaps a corpse would be re-animated; galvanism had given token of such things: perhaps the component parts of a creature might be manufactured, brought together, and endured with vital warmth.", 1818 -Mary Shelley Bioelectricity 10 Bioelectricity: Electrical charges found in cells. Especially nerve and muscle cells Biopotentials: TRANSMEMBRANE POTENTIAL Voltage difference across the cell membrane Measuring RMP 11 Measuring RMP 12 Bioelectricity 13 What contributes to generation of RMP ??? 14 1. Unequal distribution of ions across cell membrane 2. Greater membrane permeability to K+ than Na+ 3. Large indiffusible anions inside cell 4. Na+ / K+ electrogenic pump  its residues (Fig. 4C). The manner in which the 1. Unequal distribution of ions across cell membrane 15 9.2016 http://advan.physiology.org 1. Unequal distribution of ions across cell membrane Typical values 16 These differences result in a resting potential 2. Greater membrane permeability to K+ than Na+ 17  DIFFERENTIAL MEMBRANE PERMEABILITY 0.15 + - concentration 0.15 + K M M + - NaCl KCl + - electrical K+ + - + - Na+ K+ + - Potassium (K+) concentration Na+ Leak channel + - K+ electrical K++ - + - Na+ 2. Greater membrane permeability to K+ than Na+ 19 Equilibrium is reached when concentration forces are balanced by electrical forces Membrane potential is a: Diffusion potential Equilibrium Potential Resting Membrane potential is the voltage generated when the movement of all ions are at the electrochemical equilibrium What contributes to generation of RMP ??? 20 1. Net diffusion K+ out 2. Conc gradient for K+ out = Electrical Gradient pulling K+ in 3. Result is equilibrium potential Equilibrium Potential for K+ (EK+) given by Nernst Equation Nernst equation 21 [Ion] outside RxT E = 2.3026 x log ZxF [Ion] inside RxT [Ion] outside E= x ln ZxF [Ion] inside Equilibrium potential 22 RxT [Ion] outside E= x ln ZxF [Ion] inside [K+] o EK+ = 58 x ln [K+] i 4 If EM was due to K+ then it should = 58 x ln 160 equal -93mV = -93 mV Why does it not equal -70mV ??  Why is Vm so close to EK? 23 ENa+61 EK -93 Vm -70 0 mV 20 mV 130 mV If EM was due to K+ then The resting membrane potential is closest to the equilibrium it should equal -93mV potential for the ion with the highest permeability! Why does it not equal -70mV ?? Answer The membrane is far more permeable to K+ than Na+. 4. Sodium Potassium pump 24 4. Sodium Potassium pump 25 Na+ / K+ Pump Pumps 3Na+ out and 2K+ in. Inside looses 1 +Ve Becomes -Ve However remember RMP is primarily a Diffusion Potential Major role of Na+ / K+ Pump is to maintain the ionic gradients Contributes small amount approx 6 - 8mV to RMP Potentials in real cells 26 Passive distribution of K+ is NOT the only cause of the Em The membrane is RELATIVELY impermeable to Na+ NOT ABSOLUTELY impermeable to Na+ Na+/K+ ATPase (pump) Is there a an equation that allows us to predict more closely RMP ? GHK Equation 27 Better re ection of EM Takes permeability (P) into account Takes movement of all ions into account fl 28 Learning Outcomes 29 What is meant by resting membrane potential (RMP). Describe the main players in formation of RMP. Explain the formation of the nerve RMP. Explain why nerve RMP is near -70mV. Explain how potassium can kill you !!! Questions ??? 30 What is the net driving force on K+ ions? What is the net driving force on Na+ ions? Which way do the ions diffuse? What effect does increasing Na+ or K+ permeability (or extracellular concentration) have on Vm?